"The ediolon must have limbs for the synthesist to cast spells with somatic components."

and thus RAW he can cast spells despite very other spell caster requiring a free hand to cast spells.

I would interpret that the other way around: "must have limbs to cast spells", therefore: no limbs = no spell-casting.

When it comes to Eidolons, 'Limbs' has a specific meaning - arms and legs are both 'limbs' (coming from the same evolution) and thus count. This is a case where the specific trumps the general (IE, AN EIDOLON does not need an actual hand as long as it has limbs, but if it has a hand via the arms evolution, that hand does need to be free.)

"The ediolon must have limbs for the synthesist to cast spells with somatic components."

and thus RAW he can cast spells despite very other spell caster requiring a free hand to cast spells.

I would interpret that the other way around: "must have limbs to cast spells", therefore: no limbs = no spell-casting.

When it comes to Eidolons, 'Limbs' has a specific meaning - arms and legs are both 'limbs' (coming from the same evolution) and thus count.

Wow, that's correct, and kinda messed up because the intent is probably "Limbs(arms)"....

This issue only restricts a synthesist though... point being is that a Synth(serpent) would be used to casting with arms while not fused so it makes sense that his suit would need arms to continue casting.

A purely serpentine being shouldn't be required to have arms (per se) as it would be likely (save exceptionally complex somatic spells that don't exist RAW) they could have found an approximate movement. (but again, the synthesist shouldn't fall into this category unless they were serpentine to begin with - and even then RAW screws them over)

If it's going to be enforced that my eidolon has to be translucent, I'm going to push the RAW on the limbs requirement for casting.

Currently I'm running a very non-optimized build in favor of concept. If I show up to a game and am forced to abandon my concept, my next build will be a by-the-book combat optimized monster. If I have to distort RAI in favor of RAW to achieve that build, so be it.

The intent of the rule seems to be more for those that have hands to not be able to have their hands full and still cast.

Nagas are monsters, and as monsters they go under different rules than standard PC races. They can cast spells because the Bestiary says they can.

For normal PC races hand gestures, which include the manipulation of material components are the rule. IF one is going to cast spells without material components, at the very least, the Eschew Materials feat is going to be required, which shuts out any spell with expensive material components.... like Stoneskin.

For normal PC races hand gestures, which include the manipulation of material components are the RAI. IF one is going to cast spells without material components, at the very least, the Eschew Materials feat is going to be required, which shuts out any spell with expensive material components.... like Stoneskin.

If it's going to be enforced that my eidolon has to be translucent, I'm going to push the RAW on the limbs requirement for casting.

Currently I'm running a very non-optimized build in favor of concept. If I show up to a game and am forced to abandon my concept, my next build will be a by-the-book combat optimized monster. If I have to distort RAI in favor of RAW to achieve that build, so be it.

RAW Does not exist. They can only be interpreted or understood with specific intent. When the Devs give us a ruling, they are giving us their interpretation of how that rule is intended to be read. Because they are the Devs, that becomes the official interpretation. So, if in this other thread, a dev indicated that the intent of the rule was supposed to be read in a certain way, I would certainly start playing it that way in the absence of an official interpretation.